It's not because he used to chair the board meetings at the Co-operative Bank. It's not even because he is a Methodist minister. What is really startling about the footage of Paul Flowers buying cocaine and crystal meth (and opting against ketamine) is the fact that he is 63. We just don't think of older people loading up with party drugs. But should we?

As things stand, the peak age for illegal drug use is still where you would expect it to be: between a person's middle teens and their middle 20s. Currently, 8.2% of adults in England and Wales report taking an illicit drug in the past year, compared with 16.3% of those aged 16-24. "It goes along with your lifestyle," says Harry Shapiro of the charity Drugscope. "It goes along with clubbing and dancing and parties and all of that, and I suppose, in a banal way, once you get a family and a house and job things have to change."

Even so, the average age of problematic drug-users has been rising. Figures for hospital admissions where drug poisoning is the primary diagnosis show little real change among the under-35s over the past 10 years, whereas absolute numbers among the over-45s have roughly tripled since the turn of the century. To a large extent, however, this reflects the general decline of drug use among the young, and thus the gradual ageing of the small proportion who become, and stay, addicted. The story of Hans and Eva Rausing is a recent sad example.

Accordingly, while the latest British Crime Survey shows a clear pattern of falling drug-use among the young since the mid-1990s, it also shows that among 45-59-year-olds it has roughly doubled. And there are plenty more older people on the way. Between 2001 and 2031, their number is expected to rise by 50%. Having crunched the figures, a 2011 paper from the Royal College of Psychiatrists concluded that, "there is now a pressing need to address substance misuse in older people".

Naturally, it has always gone on. Jean-Paul Sartre took amphetamines almost continuously in his later years. Peter Cook was an enthusiastic cocaine-user, and ecstasy-adopter, in his 50s. But these were stark exceptions at a time when older people came from the generations who had been young in the 1950s and earlier, before drug-taking became a mainstream practice. Today's sexagenarians, by contrast, grew up in the hippy era, so it should not be a surprise if more of them carry on its practices, or revive a few.

Something else to consider is that the young people of the 70s, 80s and 90s were successively more prodigious drug-users than their forebears. You have to wonder what they will do for fun when the kids leave home and the mortgage is paid off. There may not be an army of older people out there buying drugs like the former Co-op chairman, but there may be one amassing just over the hill.